1. Field of the Invention
The invention relates to devices for infusing and removing gases from blood and more particularly relates to an outlet connector for connecting a means to remove gases from a device for infusing and removing gases from blood to a device for infusing and removing gases from blood.
2. Description of Related Art
During cardiac surgery, it is often desirable to maintain circulation of blood through a patient's body. This is often done by connecting a patient to an extra-corporeal system that adds oxygen to and removes carbon dioxide from the blood, heats or cools the blood and provides impetus to the blood to cause the blood to circulate through the patient's vascular system.
Devices, typically called oxygenators such as that shown in FIG. 1 generally labeled 2, serve the function of adding oxygen to the blood and removing carbon dioxide from the blood. Most oxygenators operate by imparting oxygen to and removing carbon dioxide from blood passing through the extra-corporeal circuit through transfer of carbon dioxide to and oxygen from a gas.
Many current oxygenators use a group of porous fibers arranged in a fiber bundle 4 as conduits for the gas used to transfer the oxygen to and carbon dioxide from the blood in the extra-corporeal circuit. In a typical design for oxygenator 2, individual fibers in fiber bundle 4 are surrounded by blood taken from a patient. The blood is removed from the venous side of a patient and is pumped through the oxygenator 2 over the fibers and is then infused into the patient's arterial side.
The venous blood from the patient has a relatively low amount of oxygen and a relatively high amount of carbon dioxide. As the blood passes through the oxygenator 2, the blood acquires oxygen from and gives up carbon dioxide to the oxygenator 2.
The typical oxygenator 2 operates by diffusing oxygen from gas in the interior passages of fibers in fiber bundle 4 through the walls of the fibers into the blood and by diffusing carbon dioxide from the blood through the walls of the fibers in the fiber bundle 4 into the interior passages of fibers in fiber bundle 4. The fibers of fiber bundle 4 are relatively porous to diffusion of oxygen and carbon dioxide across the walls of the individual fibers.
Because the partial pressure of oxygen in the gas in the fibers is higher than the partial pressure of oxygen in the blood, oxygen diffuses through the walls of the fibers from the gas in the interior of the fibers to the blood. Conversely, because the partial pressure of carbon dioxide in the blood is higher than the partial pressure of carbon dioxide in the gas in the fibers, carbon dioxide diffuses through the walls of the fibers from the blood to the gas in the interior of the fibers.
In most current oxygenators 2, the fiber bundle 4 is typically cylindrical with the individual fibers open at each end of the fiber bundle 4. Manifolds at each end of the fiber bundle 4 direct gas into and out of the fiber bundle 4 from a source of gas and to a line to vent the exhaust gas, respectively. An inlet manifold 6 at one end of the fiber bundle 4 directs gas from a source of oxygen rich gas to the open ends of the fibers in fiber bundle 4. Inlet manifold 6 has an inlet connector 8 for connecting the inlet manifold 6 to the source of oxygen rich gas.
An outlet manifold 10 is located at the end of the fiber bundle 4 opposite inlet manifold 6. Gas that has passed through the fiber bundle 4 when the oxygenator 2 is operating will have relatively higher levels of carbon dioxide and relatively lower levels of oxygen than the gas entering the fiber bundle 4. Outlet manifold 10 collects this gas that has passed through the fiber bundle 4 and directs it to a line to vent the exhaust gas.
Outlet manifold 10 has an outlet connector 12 for connecting the outlet manifold 10, through tubing, to the waste gas receptacle. Outlet connector 12 is typically hollow, substantially cylindrical and in fluid communication with outlet manifold 10. This allows a piece of tubing 14 to be connected over the outer surface 16 of outlet connector 12 so that gas can flow out of outlet manifold 10 through the hollow outlet connector 12 and through the interior of the tubing 14 to the waste gas receptacle.
Gas rich in oxygen and low in carbon dioxide enters the inlet manifold 6 through inlet connector 8, passes through the fiber bundle 4 and exits the oxygenator 2 through outlet manifold 10 and ultimately through outlet connector 12.
There are two main problems with the known outlet connectors 12. First, in order to ensure that waste gas is moved out of the oxygenator 2, the outlet connector 12 is typically connected to a source of vacuum pressure (not shown) through tubing 14 to collect and dispose of the gas. But, because the vacuum source is a negative pressure, it is possible to transfer the negative pressure to the gas in the oxygenator 2 and in particular to the gas in the fibers of the fiber bundle 4.
When the gas in the oxygenator 2 has a negative pressure, the partial pressure of oxygen in the fibers of fiber bundle 4 is reduced. Because the partial pressure of oxygen is reduced, the partial pressure differential between the oxygen in the gas in the fibers and the oxygen in the blood is reduced. As a result, less oxygen will pass from the gas to the blood thereby making the oxygenator 2 less efficient and effective as an artificial lung.
An additional problem with a negative gas pressure in the fibers of the fiber bundle 4 is that blood plasma will be pulled from the blood into the fibers thereby clogging the fibers. Clogged fibers prevent the transmission of oxygen or carbon dioxide through the clogged fibers thus making the oxygenator 2 less efficient. Further, blood plasma that is pulled into the fibers becomes damaged. These two problems with negative gas pressure are to be avoided.
A second major problem with the outlet connector 12 is that the outlet connector 12 may be mistaken for one of the other connectors on the oxygenator 2 such as are typically found. If the outlet connector 12 is mistaken for one of the other connectors, one of the operating room personnel may close the outlet connector 12 by capping it.
This problem of misidentification of outlet connector 12 is acerbated where, as commonly occurs, a heat exchanger for heating and cooling the blood passing through the oxygenator 2 is attached to or is formed in the same housing as the oxygenator 2. Heat exchangers that operate by using water to cool or heat the blood will also have at least an inlet and an outlet connector that can also be confused with outlet connector 12.
Where outlet connector 12 has been misidentified and mistakenly capped, oxygen rich gas may be applied under pressure to the oxygenator 2 through the inlet connector 8. However, because outlet connector 12 is capped, the gas will not be able to leave the oxygenator 2 through the outlet connector 12. In this case, the gas pressure in the inside the fibers in the fiber bundle 4 say rise to the input pressure of the gas at inlet connector 8. This may cause the gas under pressure in the interior of the fibers in fiber bundle 4 to be diffused across the fiber walls into the blood which is at a lower pressure. Once in the blood, this pressurized gas will expand and possibly cause embolistic problems.
Both problems of having a gas in the interior of the fibers in fiber bundle 4 that has excessively high or low pressure are to be avoided. FIG. 2 shows one way that these problems have been dealt with in the past. FIG. 2 shows an outlet connector 12 connected to an oxygenator 2. At least one small hole 18 is formed from the outer surface 16 of outlet connector 12 to the interior hollow passage (not shown). Hole 18 vents the interior hollow passage of the outlet connector 12, and consequently the interior of the oxygenator 2, to ambient pressure.
Another solution to the problem of excessively high or low gas pressure in the interior of the fibers of the fiber bundle 4 has been to place small holes in the outlet manifold 10 to vent gas pressure in the outlet manifold 10 to ambient pressure.
Although either of these approaches to solving the problem of excessively high or low gas pressure in the interior of the fibers of the fiber bundle 4 helps to prevent excessively high or low pressure in the interior of the fibers of the fiber bundle 4, neither approach helps to solve the problem of misidentifying the outlet connector 12 mentioned above.